The present invention relates to apparatus and a method for tuning a golf shaft to enable more accurate use of the assembled golf club. More particularly, use of the invention will avoid significant irregularities found in shafts made of any material including steel and composite material such as carbon fibers.
According to U.S. Pat. No. 4,958,834, a golf stroke with a club that has a shaft that has been adjusted to compensate for the presence of a seam is likely to be more accurate and will achieve greater distance. As recognized in this patent, the task of determining the location of the seam in a metal shaft is important to accomplish the object of the invention. As a first approximation, the method disclosed in the aforementioned patent improves a club""s performance by compensating for the presence of a seam with metal shafts that have a well-defined seam along the longitudinal axis of the shaft. As is well recognized, a golf swing is not an exact performance and any improvement in the club will assist a golfer generally or will reduce equipment-induced mis-hits.
The aforementioned patent describes a manual technique for determining the location of the seam in metal and composite shafts. It has become apparent, however, that this technique is only approximate and generally only locates the seam in a quadrant of the four quadrants present. With shafts made of carbon fibers and other composite materials, complications arise due to the manner in which these types of shafts are manufactured. For a large number of shafts, there is only a roughly defined seam. This results from the fact that for some shafts, several sheets of carbon fiber material are rolled typically by unskilled workers before setting the rolled sheets in an adhesive and prior to applying the surface coating. The effect is to make the definition or location of the effective seam difficult. Even were a worker to form a shaft using a single sheet of the carbon fibers, overlapping of the ends of the sheet can obscure the location of the effective seam. In this context, effective seam will be understood to mean a line extending longitudinally along the shaft surface that causes the shaft to bend and/or twist when used in a golf stroke irregularly when the effective seam is improperly positioned relative to the clubface. Of particular interest are the recently introduced filament wound shafts where a fiber strand is wrapped on a mandrel typically at a 45xc2x0 angle to the axis of the mandrel with subsequent wraps being in the opposite direction as the previous wrap. Once the adhesive and the outer coating applied an effective seam still is detectable by the method this invention.
The present invention provides a method for determining the location of the effective seam in composite material shafts as well as a metal butt-welded shaft seam with much greater precision than previous techniques. In addition, it has been discovered that the shaft of most clubs has a side or surface portion that is in compression and another side 180xc2x0 apart from the compression side that is in tension on the opposite side of a shaft. It is important according to the invention to determine which surface portion is in tension, that is, harder, and to locate that surface in a selected position relative to the clubface.
In summary, the handle end of the shaft without a cover in place is held in a grip or vise; the quadrant of the shaft containing the seam is determined by the deflection technique as described in U.S. Pat. No. 4,958,834. According to one form of the invention, the shaft is then mounted again with the end that will be attached to a club head adjacent a deflection board which is preferably provided with an electronic digital readout. The shaft when deflected in a plane will only oscillate substantially in that plane when the effective seam lies in that same plane. As noted above, according to the invention, one side of the shaft will be the tension side and the opposite side, 180xc2x0 apart on the opposite side of the shaft will be the compression side. The compression side of the shaft yields when a club head strikes a ball while the tension side is more resistant to impacts and is therefore the stronger, that is harder, side of the shaft. Preferably the tension side contains the effective seam. Pressure may be then applied to the shaft to determine which side supports the greater amount of pressure. Typically a user then selects the side that supports the greater amount of pressure to minimize the club head deflection in terms of torquing or twisting during the golf swing. As is noted in the aforementioned patent, the mounting of a club head on the shaft is then done with the face of the club pointing in a direction normal to the selected side. That is, a line perpendicular to the clubface and perpendicular to the seam on the shaft will point in the same direction. The clubface direction may be varied about the selected position to achieve desired golf shots that will fade or draw consistently. It is preferable under most circumstances that the clubface be positioned to achieve a consistently straight shot.
The foregoing and other advantages will become apparent as consideration is given to the following detailed description taken in conjunction with the accompanying drawings, in which: